// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build goexperiment.jsonv2
package json
import (
"cmp"
"errors"
"fmt"
"reflect"
"strconv"
"strings"
"sync"
"encoding/json/internal/jsonflags"
"encoding/json/internal/jsonopts"
"encoding/json/internal/jsonwire"
"encoding/json/jsontext"
)
// ErrUnknownName indicates that a JSON object member could not be
// unmarshaled because the name is not known to the target Go struct.
// This error is directly wrapped within a [SemanticError] when produced.
//
// The name of an unknown JSON object member can be extracted as:
//
// err := ...
// var serr json.SemanticError
// if errors.As(err, &serr) && serr.Err == json.ErrUnknownName {
// ptr := serr.JSONPointer // JSON pointer to unknown name
// name := ptr.LastToken() // unknown name itself
// ...
// }
//
// This error is only returned if [RejectUnknownMembers] is true.
var ErrUnknownName = errors.New("unknown object member name")
const errorPrefix = "json: "
func isSemanticError(err error) bool {
_, ok := err.(*SemanticError)
return ok
}
func isSyntacticError(err error) bool {
_, ok := err.(*jsontext.SyntacticError)
return ok
}
// isFatalError reports whether this error must terminate asharling.
// All errors are considered fatal unless operating under
// [jsonflags.ReportErrorsWithLegacySemantics] in which case only
// syntactic errors and I/O errors are considered fatal.
func isFatalError(err error, flags jsonflags.Flags) bool {
return !flags.Get(jsonflags.ReportErrorsWithLegacySemantics) ||
isSyntacticError(err) || export.IsIOError(err)
}
// SemanticError describes an error determining the meaning
// of JSON data as Go data or vice-versa.
//
// The contents of this error as produced by this package may change over time.
type SemanticError struct {
requireKeyedLiterals
nonComparable
action string // either "marshal" or "unmarshal"
// ByteOffset indicates that an error occurred after this byte offset.
ByteOffset int64
// JSONPointer indicates that an error occurred within this JSON value
// as indicated using the JSON Pointer notation (see RFC 6901).
JSONPointer jsontext.Pointer
// JSONKind is the JSON kind that could not be handled.
JSONKind jsontext.Kind // may be zero if unknown
// JSONValue is the JSON number or string that could not be unmarshaled.
// It is not populated during marshaling.
JSONValue jsontext.Value // may be nil if irrelevant or unknown
// GoType is the Go type that could not be handled.
GoType reflect.Type // may be nil if unknown
// Err is the underlying error.
Err error // may be nil
}
// coder is implemented by [jsontext.Encoder] or [jsontext.Decoder].
type coder interface{ StackPointer() jsontext.Pointer }
// newInvalidFormatError wraps err in a SemanticError because
// the current type t cannot handle the provided options format.
// This error must be called before producing or consuming the next value.
//
// If [jsonflags.ReportErrorsWithLegacySemantics] is specified,
// then this automatically skips the next value when unmarshaling
// to ensure that the value is fully consumed.
func newInvalidFormatError(c coder, t reflect.Type, o *jsonopts.Struct) error {
err := fmt.Errorf("invalid format flag %q", o.Format)
switch c := c.(type) {
case *jsontext.Encoder:
err = newMarshalErrorBefore(c, t, err)
case *jsontext.Decoder:
err = newUnmarshalErrorBeforeWithSkipping(c, o, t, err)
}
return err
}
// newMarshalErrorBefore wraps err in a SemanticError assuming that e
// is positioned right before the next token or value, which causes an error.
func newMarshalErrorBefore(e *jsontext.Encoder, t reflect.Type, err error) error {
return &SemanticError{action: "marshal", GoType: t, Err: err,
ByteOffset: e.OutputOffset() + int64(export.Encoder(e).CountNextDelimWhitespace()),
JSONPointer: jsontext.Pointer(export.Encoder(e).AppendStackPointer(nil, +1))}
}
// newUnmarshalErrorBefore wraps err in a SemanticError assuming that d
// is positioned right before the next token or value, which causes an error.
// It does not record the next JSON kind as this error is used to indicate
// the receiving Go value is invalid to unmarshal into (and not a JSON error).
func newUnmarshalErrorBefore(d *jsontext.Decoder, t reflect.Type, err error) error {
return &SemanticError{action: "unmarshal", GoType: t, Err: err,
ByteOffset: d.InputOffset() + int64(export.Decoder(d).CountNextDelimWhitespace()),
JSONPointer: jsontext.Pointer(export.Decoder(d).AppendStackPointer(nil, +1))}
}
// newUnmarshalErrorBeforeWithSkipping is like [newUnmarshalErrorBefore],
// but automatically skips the next value if
// [jsonflags.ReportErrorsWithLegacySemantics] is specified.
func newUnmarshalErrorBeforeWithSkipping(d *jsontext.Decoder, o *jsonopts.Struct, t reflect.Type, err error) error {
err = newUnmarshalErrorBefore(d, t, err)
if o.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
if err2 := export.Decoder(d).SkipValue(); err2 != nil {
return err2
}
}
return err
}
// newUnmarshalErrorAfter wraps err in a SemanticError assuming that d
// is positioned right after the previous token or value, which caused an error.
func newUnmarshalErrorAfter(d *jsontext.Decoder, t reflect.Type, err error) error {
tokOrVal := export.Decoder(d).PreviousTokenOrValue()
return &SemanticError{action: "unmarshal", GoType: t, Err: err,
ByteOffset: d.InputOffset() - int64(len(tokOrVal)),
JSONPointer: jsontext.Pointer(export.Decoder(d).AppendStackPointer(nil, -1)),
JSONKind: jsontext.Value(tokOrVal).Kind()}
}
// newUnmarshalErrorAfter wraps err in a SemanticError assuming that d
// is positioned right after the previous token or value, which caused an error.
// It also stores a copy of the last JSON value if it is a string or number.
func newUnmarshalErrorAfterWithValue(d *jsontext.Decoder, t reflect.Type, err error) error {
serr := newUnmarshalErrorAfter(d, t, err).(*SemanticError)
if serr.JSONKind == '"' || serr.JSONKind == '0' {
serr.JSONValue = jsontext.Value(export.Decoder(d).PreviousTokenOrValue()).Clone()
}
return serr
}
// newUnmarshalErrorAfterWithSkipping is like [newUnmarshalErrorAfter],
// but automatically skips the remainder of the current value if
// [jsonflags.ReportErrorsWithLegacySemantics] is specified.
func newUnmarshalErrorAfterWithSkipping(d *jsontext.Decoder, o *jsonopts.Struct, t reflect.Type, err error) error {
err = newUnmarshalErrorAfter(d, t, err)
if o.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
if err2 := export.Decoder(d).SkipValueRemainder(); err2 != nil {
return err2
}
}
return err
}
// newSemanticErrorWithPosition wraps err in a SemanticError assuming that
// the error occurred at the provided depth, and length.
// If err is already a SemanticError, then position information is only
// injected if it is currently unpopulated.
//
// If the position is unpopulated, it is ambiguous where the error occurred
// in the user code, whether it was before or after the current position.
// For the byte offset, we assume that the error occurred before the last read
// token or value when decoding, or before the next value when encoding.
// For the JSON pointer, we point to the parent object or array unless
// we can be certain that it happened with an object member.
//
// This is used to annotate errors returned by user-provided
// v2 MarshalJSON or UnmarshalJSON methods or functions.
func newSemanticErrorWithPosition(c coder, t reflect.Type, prevDepth int, prevLength int64, err error) error {
serr, _ := err.(*SemanticError)
if serr == nil {
serr = &SemanticError{Err: err}
}
var currDepth int
var currLength int64
var coderState interface{ AppendStackPointer([]byte, int) []byte }
var offset int64
switch c := c.(type) {
case *jsontext.Encoder:
e := export.Encoder(c)
serr.action = cmp.Or(serr.action, "marshal")
currDepth, currLength = e.Tokens.DepthLength()
offset = c.OutputOffset() + int64(export.Encoder(c).CountNextDelimWhitespace())
coderState = e
case *jsontext.Decoder:
d := export.Decoder(c)
serr.action = cmp.Or(serr.action, "unmarshal")
currDepth, currLength = d.Tokens.DepthLength()
tokOrVal := d.PreviousTokenOrValue()
offset = c.InputOffset() - int64(len(tokOrVal))
if (prevDepth == currDepth && prevLength == currLength) || len(tokOrVal) == 0 {
// If no Read method was called in the user-defined method or
// if the Peek method was called, then use the offset of the next value.
offset = c.InputOffset() + int64(export.Decoder(c).CountNextDelimWhitespace())
}
coderState = d
}
serr.ByteOffset = cmp.Or(serr.ByteOffset, offset)
if serr.JSONPointer == "" {
where := 0 // default to ambiguous positioning
switch {
case prevDepth == currDepth && prevLength+0 == currLength:
where = +1
case prevDepth == currDepth && prevLength+1 == currLength:
where = -1
}
serr.JSONPointer = jsontext.Pointer(coderState.AppendStackPointer(nil, where))
}
serr.GoType = cmp.Or(serr.GoType, t)
return serr
}
// collapseSemanticErrors collapses double SemanticErrors at the outer levels
// into a single SemanticError by preserving the inner error,
// but prepending the ByteOffset and JSONPointer with the outer error.
//
// For example:
//
// collapseSemanticErrors(&SemanticError{
// ByteOffset: len64(`[0,{"alpha":[0,1,`),
// JSONPointer: "/1/alpha/2",
// GoType: reflect.TypeFor[outerType](),
// Err: &SemanticError{
// ByteOffset: len64(`{"foo":"bar","fizz":[0,`),
// JSONPointer: "/fizz/1",
// GoType: reflect.TypeFor[innerType](),
// Err: ...,
// },
// })
//
// results in:
//
// &SemanticError{
// ByteOffset: len64(`[0,{"alpha":[0,1,`) + len64(`{"foo":"bar","fizz":[0,`),
// JSONPointer: "/1/alpha/2" + "/fizz/1",
// GoType: reflect.TypeFor[innerType](),
// Err: ...,
// }
//
// This is used to annotate errors returned by user-provided
// v1 MarshalJSON or UnmarshalJSON methods with precise position information
// if they themselves happened to return a SemanticError.
// Since MarshalJSON and UnmarshalJSON are not operating on the root JSON value,
// their positioning must be relative to the nested JSON value
// returned by UnmarshalJSON or passed to MarshalJSON.
// Therefore, we can construct an absolute position by concatenating
// the outer with the inner positions.
//
// Note that we do not use collapseSemanticErrors with user-provided functions
// that take in an [jsontext.Encoder] or [jsontext.Decoder] since they contain
// methods to report position relative to the root JSON value.
// We assume user-constructed errors are correctly precise about position.
func collapseSemanticErrors(err error) error {
if serr1, ok := err.(*SemanticError); ok {
if serr2, ok := serr1.Err.(*SemanticError); ok {
serr2.ByteOffset = serr1.ByteOffset + serr2.ByteOffset
serr2.JSONPointer = serr1.JSONPointer + serr2.JSONPointer
*serr1 = *serr2
}
}
return err
}
// errorModalVerb is a modal verb like "cannot" or "unable to".
//
// Once per process, Hyrum-proof the error message by deliberately
// switching between equivalent renderings of the same error message.
// The randomization is tied to the Hyrum-proofing already applied
// on map iteration in Go.
var errorModalVerb = sync.OnceValue(func() string {
for phrase := range map[string]struct{}{"cannot": {}, "unable to": {}} {
return phrase // use whichever phrase we get in the first iteration
}
return ""
})
func (e *SemanticError) Error() string {
var sb strings.Builder
sb.WriteString(errorPrefix)
sb.WriteString(errorModalVerb())
// Format action.
var preposition string
switch e.action {
case "marshal":
sb.WriteString(" marshal")
preposition = " from"
case "unmarshal":
sb.WriteString(" unmarshal")
preposition = " into"
default:
sb.WriteString(" handle")
preposition = " with"
}
// Format JSON kind.
switch e.JSONKind {
case 'n':
sb.WriteString(" JSON null")
case 'f', 't':
sb.WriteString(" JSON boolean")
case '"':
sb.WriteString(" JSON string")
case '0':
sb.WriteString(" JSON number")
case '{', '}':
sb.WriteString(" JSON object")
case '[', ']':
sb.WriteString(" JSON array")
default:
if e.action == "" {
preposition = ""
}
}
if len(e.JSONValue) > 0 && len(e.JSONValue) < 100 {
sb.WriteByte(' ')
sb.Write(e.JSONValue)
}
// Format Go type.
if e.GoType != nil {
typeString := e.GoType.String()
if len(typeString) > 100 {
// An excessively long type string most likely occurs for
// an anonymous struct declaration with many fields.
// Reduce the noise by just printing the kind,
// and optionally prepending it with the package name
// if the struct happens to include an unexported field.
typeString = e.GoType.Kind().String()
if e.GoType.Kind() == reflect.Struct && e.GoType.Name() == "" {
for i := range e.GoType.NumField() {
if pkgPath := e.GoType.Field(i).PkgPath; pkgPath != "" {
typeString = pkgPath[strings.LastIndexByte(pkgPath, '/')+len("/"):] + ".struct"
break
}
}
}
}
sb.WriteString(preposition)
sb.WriteString(" Go ")
sb.WriteString(typeString)
}
// Special handling for unknown names.
if e.Err == ErrUnknownName {
sb.WriteString(": ")
sb.WriteString(ErrUnknownName.Error())
sb.WriteString(" ")
sb.WriteString(strconv.Quote(e.JSONPointer.LastToken()))
if parent := e.JSONPointer.Parent(); parent != "" {
sb.WriteString(" within ")
sb.WriteString(strconv.Quote(jsonwire.TruncatePointer(string(parent), 100)))
}
return sb.String()
}
// Format where.
// Avoid printing if it overlaps with a wrapped SyntacticError.
switch serr, _ := e.Err.(*jsontext.SyntacticError); {
case e.JSONPointer != "":
if serr == nil || !e.JSONPointer.Contains(serr.JSONPointer) {
sb.WriteString(" within ")
sb.WriteString(strconv.Quote(jsonwire.TruncatePointer(string(e.JSONPointer), 100)))
}
case e.ByteOffset > 0:
if serr == nil || !(e.ByteOffset <= serr.ByteOffset) {
sb.WriteString(" after offset ")
sb.WriteString(strconv.FormatInt(e.ByteOffset, 10))
}
}
// Format underlying error.
if e.Err != nil {
errString := e.Err.Error()
if isSyntacticError(e.Err) {
errString = strings.TrimPrefix(errString, "jsontext: ")
}
sb.WriteString(": ")
sb.WriteString(errString)
}
return sb.String()
}
func (e *SemanticError) Unwrap() error {
return e.Err
}
func newDuplicateNameError(ptr jsontext.Pointer, quotedName []byte, offset int64) error {
if quotedName != nil {
name, _ := jsonwire.AppendUnquote(nil, quotedName)
ptr = ptr.AppendToken(string(name))
}
return &jsontext.SyntacticError{
ByteOffset: offset,
JSONPointer: ptr,
Err: jsontext.ErrDuplicateName,
}
}
